1.\" $OpenBSD: acpicpu.4,v 1.10 2022/10/21 04:02:16 guenther Exp $ 2.\" 3.\" Copyright (c) 2006 Michael Knudsen <mk@openbsd.org> 4.\" 5.\" Permission to use, copy, modify, and distribute this software for any 6.\" purpose with or without fee is hereby granted, provided that the above 7.\" copyright notice and this permission notice appear in all copies. 8.\" 9.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES 10.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF 11.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR 12.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES 13.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN 14.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF 15.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. 16.\" 17.Dd $Mdocdate: October 21 2022 $ 18.Dt ACPICPU 4 19.Os 20.Sh NAME 21.Nm acpicpu 22.Nd ACPI processor power and performance state 23.Sh SYNOPSIS 24.Cd "acpicpu* at acpi?" 25.Sh DESCRIPTION 26The 27.Nm 28driver provides support for extracting processor power and performance 29levels from ACPI tables. 30This information is used to enter deeper CPU power states when idle, 31and can be used to throttle processor speed to reduce 32power usage and extend battery life through the 33.Va hw.setperf 34.Xr sysctl 2 35mechanism. 36.Pp 37.Nm 38reports the C-states offered by ACPI using the format 39.Dl C%d(%d@%d %s.%x@%#x) 40where the respective fields are the ACPI state, 41the reported power consumption, 42the reported latency, 43the method, 44the flags on the method, 45and the address for the method. 46Inapplicable or unspecified fields are elided. 47If the state won't be used for any reason then the entry will have a 48.Sq !\& 49prefix. 50If the state is the fallback state used when no valid C-state entries were 51found then flags will be a 52.Sq !\& . 53For the 54.Va mwait 55method the address is the hints value for the instruction. 56.Sh SEE ALSO 57.Xr sysctl 2 , 58.Xr acpi 4 , 59.Xr cpu 4 , 60.Xr intro 4 , 61.Xr apmd 8 , 62.Xr sysctl 8 63.Sh HISTORY 64The 65.Nm 66driver first appeared in 67.Ox 3.9 . 68.Sh AUTHORS 69.An -nosplit 70The 71.Nm 72driver was written by 73.An Marco Peereboom Aq Mt marco@openbsd.org . 74CPU power state (C-state) support was added by 75.An Philip Guenther Aq Mt guenther@openbsd.org . 76